1. Field of the Invention
The present invention relates to a waste water treatment apparatus for efficiently treat a waste water containing an organic matter and/or an inorganic matter. More particularly, the invention relates to a compact waste water treatment apparatus constituted by at least a waste water treatment tank comprising a denitrification tank and/or a nitrification tank to which a carrier particle immobilizing a microbe is charged and a membrane module, and a waste water treatment apparatus comprising at least a waste water treatment tank for decomposing and eliminating an organic matter and/or an inorganic matter contained in the waste water, in which a carrier formed by immobilizing a microbe to an acetalized polyvinyl alcohol hydrogel is charged to said waste water treatment tank.
2. Description of the Prior Art
Conventionally, an organic waste water including a nitrogenous substance such as a waste water in a farm village, a waste water for domestic use, an urban sewage, a waste water in a fish farming, and a waste water in various kinds of industries has been generally treated in accordance with an activated sludge method for purifying a polluted sludge by using an aerobic microbe and an anaerobic microbe. For example, as shown in FIG. 12, a waste water 1 is flowed into an anaerobic filtration tank 32, next, an oxidation of a BOD component and a nitrification of a nitrogenous substance by means of a nitrifying bacteria are performed under an aerobic condition in an aerobic filtration tank 33, a part of a treated water flowing out from the aerobic filtration tank 33 is circulated to the anaerobic filtration tank 32, a denitrification and elimination is performed by using denitrifying bacteria under an anaerobic condition, in the remaining flowing water from the aerobic filtration tank, the polluted sludge is settled and separated in a precipitation tank 34, and thereafter, a supernatant liquid 26 is discharged.
In the case of the conventional activated sludge method, a residence time of the waste water in an aeration tank is designed to be six to eight hours, however, an amount of the waste water recently tends to increase in correspondence to a variation of the industry and life, so that when a large amount of waste water is going to be treated in accordance with the activated sludge method by using the conventional treatment tank, an abnormality such as a bulking is generated because a residence time becomes short, and a satisfactory treatment can not be performed. Accordingly, in order to correspond to the treatment of a large amount of waste water, a new apparatus is required, so that a vast ground and an expensive building cost are required.
On the contrary, in view of elimination of a nitrogen, the conventional nitrogen elimination is performed by a treatment method constituted by introducing a water to be treated to the denitrification tank and the nitrification tank in the order, returning and circulating a part of the nitrified water flowing out from the nitrification tank to the denitrification tank, and sending the remaining nitrified water to a final precipitation pool, or a treatment method constituted by introducing to the nitrification tank and the denitrification tank in the order, and sending all amount of the denitrified water flowing out from the denitrification tank to a final precipitation pool. At this time, in the nitrification tank, a Kjeldahl nitrogen is oxidized to a nitrite nitrogen or a nitrate nitrogen, and in the denitrification tank, a nitrite nitrogen or a nitrate nitrogen is converted to a gaseous nitrogen so as to be eliminated, however, in these methods, it is general to eliminate a nitrogen by nitrifying and denitrifying by means of an activated sludge.
Even in the case that the waste water is treated by such a nitrogen eliminating method, a total residence time in the nitrification tank and the denitrification tank requires twelve to twenty-four hours on the basis of the flowing-in water, so that in a conventional sewage treatment plant having a purpose of only eliminating the BOD and designed to have a residence time of about six to eight hours, the residence time is insufficient and a satisfactory elimination of a nitrogen can not be performed. In order to correspond to a treatment of a lot of water, in the same manner as mentioned above, a new treatment apparatus is required, so that a vast ground and an expensive building cost are required.
On the contrary, in order to shorten a time for a treatment and make a treatment stable and a high level, with the object of increasing a concentration of a microbe within the waste water treatment tank and increasing a residence time of the microbe, a method of and an apparatus for treating by using a microbe carrier have been developed. As an example of this kind, in Japanese Patent Examined Publication No. 59-16516, there is disclosed a fluidized bed biological treatment method and an apparatus therefor which is structured such as to eliminate an organic matter contained in the waste water by fluidizing the carrier, and in Japanese Patent Examined Publication No. 63-52556, there is disclosed a method of biologically treating a waste water by charging a carrier in which an activated sludge is inclusively immobilized to a polymeric carrier in a waste water treatment tank and making them contact under a aerobic condition.
As another example, in Japanese Patent Examined Publication No. 1-37988, Japanese Patent Examined Publication No. 2-7716, Japanese Patent Unexamined Publication No. 4-310298, Japanese Patent Unexamined Publication No. 7-68282 and Japanese Patent Unexamined Publication No. 7-68287, there is disclosed a method of and an apparatus for treating a waste water using by charging a carrier in which a denitrifying bacteria and a nitrifying bacteria is inclusively immobilized to a polymeric carrier in an anaerobic filtration tank and an aerobic filtration tank.
In recent years, a consideration of making a waste water treatment apparatus compact by charging a carrier in which a microbe is attached and increased to a treatment tank has been promoted, so that granules such as various kinds of ceramics and plastics and a honeycomb construction body serving as a carrier have been developed. As a carrier used for a waste water treatment, an increase of a water content, an excellence of a permeability with respect to an oxygen and a substrate, and an increase of an affinity with an organism are required. In this view, there has been known a hydrogel obtained by, for example, a method of partially dehydrating a freezing portion after charging a polyvinyl alcohol aqueous solution (hereinafter, a polyvinyl alcohol is called PVA for short) into a mold (Japanese Patent Unexamined Publication No. 58-36630), a method of gelling by bringing a PVA aqueous solution into contact with a saturated boric acid aqueous solution ("Journal of Japan Sewage Works Association", Vol.23, p41(1986); "Journal of Water and Waste", Vol.30, p36 (1986)), a method of defrosting a freezing after a mixed aqueous solution of a PVA and a sodium alginate is brought into contact with a calcium chloride aqueous solution so as to spheroidize (Japanese Patent Unexamined Publication No. 64-43188), and a method of acetalizing by formaldehyde (Japanese Patent Unexamined Publication No. 7-41516).
On the contrary, in correspondence to a development of a membrane separating technology, a frequency of using a separating membrane has been increased for the purpose of increasing a quality of a treated water. As an example, in Japanese Patent Examined Publication No. 64-5960, there is disclosed a waste water treatment apparatus for performing a filtration treatment by communicating a hollow fiber membrane module with a bottom surface of a treatment tank, and in Japanese Patent Examined Publication No. 64-9071, there is disclosed a waste water treatment apparatus for performing a filtration treatment by arranging a hollow fiber membrane module above a treatment tank.
Further, a system for efficiently performing a waste water treatment by circulating a water to be treated is also considered, for example, in Japanese Patent Examined Publication No. 64-9074, there is disclosed a waste water treatment apparatus structured such that in a treatment tank comprising an anaerobic filtration tank and an aerobic filtration tank having a membrane module above aeration means, a part of a treated water from the aerobic filtration tank is returned to the anaerobic filtration tank.
However, in any of these, since the membrane module is provided within the treatment tank, the settling sludge treated by the polymeric carrier tends to be attached to the surface of the membrane and the portion between the hollow fiber membrane bundles, thereby clogging the pores of the membrane a load of a waste water flow amount can not be set to be a high value, so that a compactification of the apparatus has been limited. Further, a crack and a breakage have been easily generated by a geometrical effect of an attachment of a settling sludge to a membrane surface, a vibration by an air for an aeration and a collision of a carrier particle.
On the contrary, in a system of circulating a water to be treated, there is also disclosed an apparatus in which a membrane module is provided in an outer portion of a treatment tank, for example, in Japanese Patent Examined Publication No. 6-45035, there is disclosed a waste water treatment method constituted by at first treating a waste liquid in a bioreactor (I) using a denitrifying bacteria, next treating in a bioreactor (II) using a BOD oxidizing bacteria and a nitrifying bacteria, further introducing the treated liquid to a membrane separation apparatus, and respectively circulating a non-permeating liquid not passing through the membrane and a permeating liquid passing through the membrane to said bioreactor (II) and the bioreactor (I).
Further, in Japanese Patent Unexamined Publication No. 4-200697, there is disclosed a treatment apparatus for an organic waste water constituted by a circulating type organism treatment apparatus comprising an air lift type fluidized tank performing a treatment by fluidizing granulous microbe carrier and an expansion type fluidized tank, and a ultrafiltration membrane apparatus, and pressing a part of or all of the circulating water from the ultrafiltration membrane apparatus into a bottom portion of the expansion type fluidized bed.
However, in the method disclosed in Japanese Patent Examined Publication No. 6-45035, although the membrane module is disposed in the outer portion of the treatment tank, a concentration of a floating activated sludge containing a nitrifying bacteria is high, so that there is a disadvantage that the membrane is still easily closed. Further, in the treatment apparatus disclosed in Japanese Patent Unexamined Publication No. 4-200697, although a part of or all of the circulating water from the ultrafiltration apparatus is pressed into the bottom portion of the expansion type fluidized tank (the denitrification tank), the flow amount is limited in such a manner that the microbe carrier does not overflow, so that there is a disadvantage that a fluidity of the carrier is insufficient and a denitrification performance is deteriorated. Further, in the case that a circulating amount of the liquid is much, a concentration of a dissolved oxygen in the tank becomes high, so that the denitrification performance is deteriorated.
Each of the waste water treatment apparatus using the membrane mentioned above is useful for making the apparatus compact at a certain degree, however, in this kind of apparatus, as a combined purification tank is represented, a structure which is significantly compact, has an excellent durability and can increase a quality of the water to be treated has been required, but there has been yet no waste water treatment apparatus which satisfied the above points.
Further, in the waste water treatment, a bad smell is frequently generated, and this is pointed out as a new problem on environment. In the conventional waste water treatment method using the carrier, although a waste water treatment performance is sufficient, a bad smell can not be removed, so that a countermeasure such that a bad smell treatment apparatus is independently provided has been required. Accordingly, also in view of a bad smell, a carrier which does not make the apparatus big and is economically advantageous is desired.